The purpose of this activity is for students to transition from expressing the length of objects as a count of physical length units (for example, 12 cubes) to expressing the length of objects using a standard unit (for example, 12 centimeters). Students use centimeter cubes and 10-centimeter tools (base-ten blocks) to measure the length of an earthworm. Throughout the activity, students make connections to place value and describe the convenience of different types of tools based on their length (MP5).

• Share and display student measurements for the last problem.
• As needed, select previously identified students to demonstrate their responses to the following discussion questions.
• “How can you prove that the bearded dragon is 24 centimeters long with only centimeter cubes?” (Start at one end and line up the cubes until you reach the other end. You can count the cubes because each cube is 1 centimeter long.)
• “How can you prove the bearded dragon is 24 cm long with 10-centimeter tools?” (Start at one end with one 10-centimeter tool, then keep lining up more 10-centimeter tools until you go past the end. You can count the first two by 10, then start counting by ones until you get to the block that lines up with the end.)
• “Which tool was easier to use to measure the length of the bearded dragon?” (I liked using the 10-centimeter tools because you could measure faster without having to use as many blocks. It was easier to count.)

The purpose of this activity is for students to practice measuring and expressing the length of objects in centimeters. Students measure the length of different reptiles and choose whether to use centimeter cubes, 10-centimeter tools, or a combination of the two tools (MP5). Students may also choose whether to compare the length of the day gecko and the threadsnake by measuring the difference in lengths directly or by measuring each reptile and finding the difference. Students have more opportunities to explore these approaches in future lesson activities.

• “How did you decide which tools to use to measure the ____?”
• “How could you use the 10-centimeter tool to measure the next reptile? How could you use both tools to measure?”

• Invite previously identified students to share how they measured a length that was shorter than 10 cm (A or E).
• Invite previously identified students to share how they measured a length longer than 10 cm (B, C, D, or F).